How to fail over connection even if interface is stll up/up?

Unanswered Question
Nov 12th, 2008

I have a Cisco router connected to an Internet T1 and an Internet DSL line, NATting to each connection and sending certain traffic through each connection via route-maps. If the T1 or DSL is unplugged from the router, all of the traffic "fails over" to the other connection. Is there any way to automatically have traffic "fail over" from a malfunctioning connection if the connection is still up/up (but possibly just not passing traffic?). Having the ability to ping a remote host through each connection to determine that connection's availability would be ideal.

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (1 ratings)
scottmac Wed, 11/12/2008 - 17:23

About the only way would be to create a tunnel (like GRE tunnel) between your site and some other site.

Trigger your actions on the broken tunnel.

Good Luck

jasonww04 Mon, 11/17/2008 - 12:52

That seems to only be useful if all the traffic is going through a VPN tunnel. I have one interface set up for traffic going to my data center and the other interface is for all other traffic. I would like to have all traffic go to one interface is the other fails. Does that make sense?

Edison Ortiz Mon, 11/17/2008 - 13:00

That seems to only be useful if all the traffic is going through a VPN tunnel.

Sorry, that's not correct.

IP SLA is useful over any type of media and it determines if the remote end is reachable via a specified interface.

You can also use dynamic routing protocol end-to-end and depending on the protocol of choice, you can setup routing preferences by using one link over the other.

I highly recommend exploring the dynamic routing protocol approach as it's more scalable and resilient.




Richard Burts Mon, 11/17/2008 - 13:30


While I agree with Edison that if it is available the dynamic routing option has advantages in scalability and resilience, sometimes the routing option is not available. Given your description of an Internet T1 and a DSL I am guessing that this might be one of the times that dynamic routing is not a good option.

In which case the IP SLA ought to do what you want. I recently configured IP SLA for a customer whose requirements were similar to yours as far as I can tell. We configured a static default route to handle most traffic and a floating static default route to handle the situation if the primary default route failed. We configured alternate routing for some traffic using the alternate interface. We configured IP SLA to monitor access through the FastEthernet and remove routes if the interface stayed up/up but we lost responses through it. I believe that a similar approach should work for you.



jasonww04 Mon, 11/17/2008 - 13:41

It took me a little bit to grasp the IP SLA but I think that is what we are going to try. I'm just a little hard pressed to figure out how to configure it for the interface that handles non-specific traffic (the DSL interface). The interface for my data center seems pretty straight forward.


This Discussion